Endogenous tissue engineering: PTH therapy for skeletal repair

Based on its proven anabolic effects on bone in osteoporosis patients, recombinant parathyroid hormone (PTH_1-34) has been evaluated as a potential therapy for skeletal repair. In animals, the effect of PTH_1-34 has been investigated in various skeletal repair models such as fractures, allografting, spinal arthrodesis and distraction osteogenesis. These studies have demonstrated that intermittent PTH_1-34 treatment enhances and accelerates the skeletal repair process via a number of mechanisms, which include effects on mesenchymal stem cells, angiogenesis, chondrogenesis, bone formation and resorption. Furthermore, PTH_1-34 has been shown to enhance bone repair in challenged animal models of aging, inflammatory arthritis and glucocorticoid-induced bone loss. This pre-clinical success has led to off-label clinical use and a number of case reports documenting PTH_1-34 treatment of delayed-unions and non-unions have been published. Although a recently completed phase 2 clinical trial of PTH_1-34 treatment of patients with radius fracture has failed to achieve its primary outcome, largely because of effective healing in the placebo group, several secondary outcomes are statistically significant, highlighting important issues concerning the appropriate patient population for PTH_1-34 therapy in skeletal repair. Here, we review our current knowledge of the effects of PTH_1-34 therapy for bone healing, enumerate several critical unresolved issues (e.g., appropriate dosing regimen and indications) and discuss the long-term potential of this drug as an adjuvant for endogenous tissue engineering.     

The risks of using the chi-square periodogram to estimate the period of biological rhythms

The chi-square periodogram (CSP), developed over 40 years ago, continues to be one of the most popular methods to estimate the period of circadian (circa 24-h) rhythms. Previous work has indicated the CSP is sometimes less accurate than other methods, but understanding of why and under what conditions remains incomplete. Using simulated rhythmic time-courses, we found that the CSP is prone to underestimating the period in a manner that depends on the true period and the length of the time-course. This underestimation bias is most severe in short time-courses (e.g., 3 days), but is also visible in longer simulated time-courses (e.g., 12 days) and in experimental time-courses of mouse wheel-running and ex vivo bioluminescence. We traced the source of the bias to discontinuities in the periodogram that are related to the number of time-points the CSP uses to calculate the observed variance for a given test period. By revising the calculation to avoid discontinuities, we developed a new version, the greedy CSP, that shows reduced bias and improved accuracy. Nonetheless, even the greedy CSP tended to be less accurate on our simulated time-courses than an alternative method, namely the Lomb-Scargle periodogram. Thus, although our study describes a major improvement to a classic method, it also suggests that users should generally avoid the CSP when estimating the period of biological rhythms.     

Development of species-specific primers for rapid identification by PCR of the ecologically important pathogen Fusarium keratoplasticum from isolated and environmental samples

The genus Fusarium contains many fungal species known to be pathogenic to animals and plants alike. One species complex within this genus, the Fusarium solani species complex (FSSC), is of particular concern due to its high numbers of pathogenic members. FSSC members are known to contribute significantly to plant, human and other animal fungal disease. One member of the FSSC, Fusarium keratoplasticum, is of particular ecological concern and has been implicated in low hatching success of endangered sea turtle eggs, as well as contribute to human and other animal Fusarium pathogenesis. Species-specific primers for molecular identification of F. keratoplasticum currently do not exist to our knowledge, making rapid identification, tracking and quantitation of this pathogenic fungus difficult. The objective of this study was to develop primers specific to F. keratoplasticum that could be applied to DNA from isolated cultures as well as total (mixed) DNA from environmental samples. RPB2 sequence from 109 Fusarium isolates was aligned and analysed to determine nucleotide polymorphisms specific to F. keratoplasticum useful for primer design. A set of primers were generated and found to be effective for identification of F. keratoplasticum from total DNA extracted from sand surrounding sea turtle nesting sites.     

Improving acclimatization through the photoautotrophic culture of coconut (Cocos nucifera) seedlings: an in vitro system for the efficient exchange of germplasm

An in vitro photoautotrophic step based on the supply of CO₂-enriched air (1,600 μmol mol^?1) during the light phase and ambient air (350 μmol mol^?1 CO₂) during the dark phase has been used to promote the ex vitro establishment of coconut (Cocos nucifera L.) seedlings. The introduction of this step into a previously developed in vitro protocol was found to improve the quality of the seedlings (as assessed by fresh weight increase, physical stature, leaf area and thickness, stomatal density, and chlorophyll a content, and primary and secondary root production), the proportion of seedlings successfully transferred to soil (improvement from 40% to 100%) and achieved in a shorter time (reduction from 10 to 6 mo). Best results using this photoautotrophic growth step were obtained when a low medium concentration of sucrose (43.8 mM or lower) was used, when it was applied to seedlings that had already reached 4 or 5 mo of age in the in vitro culture step, and when seedlings were cultured in the photoautotrophic system for 2 mo or more before transfer to soil. Our improved protocol is more efficient and it reduces the cost per plant for the international exchange of coconut germplasm.     

HlyC, the internal protein acyltransferase that activates hemolysin toxin: the role of conserved tyrosine and arginine residues in enzymatic activity as probed by chemical modification and site-directed mutagenesis.

Internal fatty acylation of proteins is a recognized means of modifying biological behavior. Escherichia coli hemolysin A (HlyA), a toxic protein, is transcribed as a nontoxic protein and made toxic by internal acylation of two lysine residue epsilon-amino groups; HlyC catalyzes the acyl transfer from acyl-acyl carrier protein (ACP), the obligate acyl donor. Conserved residues among the respective homologous C proteins that activate 13 different RTX (repeats in toxin) toxins of which HlyA is the prototype likely include some residues that are important in catalysis. Possible roles of two conserved tyrosines and two conserved arginines were investigated by noting the effects of chemical modifiers and site-directed mutagenesis. TNM modification of HlyC at pH 8.0 led to extensive inhibition that was prevented by the presence of the substrate myristoyl-ACP but not by the product, ACPSH. NAI had no effect. Y70G and Y150G greatly diminished enzyme activity, whereas mutations Y70F and Y150F exhibited wild-type activity. Modification of arginine residues with PG markedly lowered acyltransferase activity with moderate protection by both myristoyl-ACP and ACPSH. Under optimum conditions, four separate mutations of the two conserved arginine residues (R24A, R24K, R87A, and R87K) had little effect on acyltransferase activity.     

Crystal structure of a novel mid-gut procarboxypeptidase from the cotton pest Helicoverpa armigera.

The cotton bollworm Helicoverpa armigera (Hubner) (Lepidoptera: Noctuidae) is one of the most serious insect pests in Australia, India and China. The larva causes substantial economical losses to legume, fibre, cereal oilseed and vegetable crops. This pest has proven to be difficult to control by conventional means, mainly due to the development of pesticide resistance. We present here the 2.5 A crystal structure from the novel procarboxypeptidase (PCPAHa) found in the gut extracts from H. armigera larvae, the first one reported for an insect. This metalloprotease is synthesized as a zymogen of 46.6 kDa which, upon in vitro activation with Lys-C endoproteinase, yields a pro-segment of 91 residues and an active carboxypeptidase moiety of 318 residues. Both regions show a three-dimensional structure quite similar to the corresponding structures in mammalian digestive carboxypeptidases, the most relevant structural differences being located in the loops between conserved secondary structure elements, including the primary activation site. This activation site contains the motif (Ala)(5)Lys at the C terminus of the helix connecting the pro- and the carboxypeptidase domains. A remarkable feature of PCPAHa is the occurrence of the same (Ala)(6)Lys near the C terminus of the active enzyme. The presence of Ser255 in PCPAHa instead of Ile and Asp found in the pancreatic A and B forms, respectively, enlarges the S1' specificity pocket and influences the substrate preferences of the enzyme. The C-terminal tail of the leech carboxypeptidase inhibitor has been modelled into the PCPAHa active site to explore the substrate preferences and the enzymatic mechanism of this enzyme.     

Immunologic and nonimmunologic responsiveness in ragweed-sensitized dogs

The relationship between airway responsiveness to inhaled antigen and histamine, immunologic release of lung histamine, immunologic responsiveness of skin, and specific immunoglobulin E (IgE) antibodies were examined in 11 inbred allergic dogs immunized with extracts of ragweed and grass and 5 nonimmunized control dogs from the same colony. Airway responsiveness to antigen and histamine was characterized by the doses that increased the airflow resistance of the total respiratory system to twice the control values (ED200). Highly significant correlations were found between airway responsiveness and cutaneous responsiveness to antigen and other immunologic characteristics (e.g., IgE and histamine released from lung by inhaled antigen) in all dogs. In ragweed-sensitized dogs, there was an inverse correlation between immunologic responsiveness (reflected by the cutaneous response to antigen and histamine released from lung by inhaled antigen) and nonimmunologic responsiveness of airways (histamine ED200: r = 0.73, P less than 0.05 and r = 0.75, P less than 0.01, respectively). Antigen ED200 was also correlated with histamine release from lung after antigen inhalation (r = 0.74; P less than 0.01). We conclude that airway reactions to inhaled antigen in allergic dogs are dependent not only on immunologic factors but also on the degree of nonimmunologic airway responsiveness to histamine and that these factors are correlated inversely.     

Group versus population level demographics: An analysis of comparability using long term data on wild white‐faced capuchin monkeys (Cebus capucinus imitator)

Primates have long been used as indicator species for assessing overall ecosystem health. However, area‐wide census methods are time consuming, costly, and not always feasible under many field conditions. Therefore, it is important to establish whether monitoring a subset of a population accurately reflects demographic changes occurring in the population at large. Over the past 35 years, we have conducted 15 area‐wide censuses in Sector Santa Rosa, Costa Rica. These efforts have revealed important trends in population growth patterns of capuchin monkeys following the protection and subsequent regeneration of native forests. During this same period, we have also intensively studied a subset of the capuchin groups. Comparing these two datasets, we investigate whether the population structures of the closely monitored groups are reliable indicators of area‐wide demographic patterns. We compare the overall group size and the individual age/sex class compositions of study groups and nonstudy groups (i.e., those contacted during area‐wide censuses only). Our study groups contained more individuals overall with a larger proportion of infants, and there were indications that the proportion of adult and subadult males was lower. These differences can be ascribed either to sampling errors or real differences attributable to human presence and/or better habitat quality for the study groups. No other sex/age classes differed, and major demographic changes were simultaneously evident in both study and nonstudy groups. This study suggests that the Santa Rosa capuchin population is similarly impacted by large‐scale ecological patterns observable within our study groups.     

Third trimester placental grading by ultrasonography as a test of fetal wellbeing.

In a study of 2000 unselected pregnant women the development of a mature placental appearance (grade 3) on ultrasonography by 34-36 weeks'' gestation, observed in 15% of cases, was associated with maternal smoking, low parity, low maternal age, and being white. These women had an increased risk of problems during labour and their babies had an increased risk of low birth weight, poor condition at birth, and perinatal death. The women were randomly allocated to two groups: in one group the result of the placental grading was reported to the clinician responsible for care; in the second the result was noted but not reported. There was a significant decrease in the risk of perinatal death in the group where the grading was known. This reduction was responsible for a difference in the principal outcome index, a heterogeneous group of measures of mortality and morbidity, but this difference was not significant. This study alone does not justify routine late scanning, and further, larger trials are required. Nevertheless, the results do provide a basis for the reporting of placental grading when ultrasound examination is performed during the third trimester.